About

Stephen Riser is an oceanographer with long-term interests in the interactions of the physical and chemical aspects of the circulation of the large-scale ocean. He focuses on the use of profiling float technology to study ocean circulation at a global level, and his laboratory has built and deployed over 1400 floats in the past decade in support of these studies. With his laboratory, he has also pioneered the use of many of the technologies presently used in modern profiling floats, including the addition of biogeochemical sensors, under-ice technology, and the use of Iridium communications.

Research topics

• Oceanography
• Geology
• Climatology
• Environmental science
• Ecology
• Chemistry
• Atmospheric sciences
• Geography
• Environmental chemistry
• Meteorology
• Physics

Selected publications

• SOCCOM and GO-BGC float data - Snapshot 2025-12-21. In Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) and Global Ocean Biogeochemistry (GO-BGC) Biogeochemical-Argo Float Data Archive

  California Digital Library · 2025-12-21

  datasetOpen access

  This .zip archive contains Quality Controlled float data for biogeochemical profiling floats deployed by the Southern Ocean Carbon and Climate Observation and Modeling (SOCCOM) and Global Ocean Biogeochemistry Array (GO-BGC) projects. Additional University of Washington/MBARI floats deployed outside of these programs have also been included in the archive. Data for all floats within this archive were processed by the float data management team at the Monterey Bay Aquarium Research Institute (MBARI). A comprehensive listing of floats processed by MBARI (including internal floatID, WMOID, float platform type, and program) is included within each archive. Note that historical snapshots, frozen prior to December 2022, can be found under the SOCCOM collection (https://doi.org/10.6075/J0TX3C9X). FORMAT: The ascii files contained herein were formatted to be compatible with Ocean Data View (ODV). Character encoding is UTF-8. ODV is freely available at https://odv.awi.de/. In addition, a Matlab function has been provided in each .zip archive for parsing the .txt files into data structures within Matlab (see get_FloatViz_data.m). Please note that the data files within this .zip archive represent a snapshot of all SOCCOM and GO-BGC float data processed at MBARI as of the date listed in the file name. Therefore, be aware that processing updates (** AND THUS CHANGES TO THE DATA **) may have occurred since the time the snapshot was created. For the most up-to-date files (processed every 4 hours), visit https://ftp.mbari.org/pub/SOCCOM/FloatVizData/ or https://www.mbari.org/science/upper-ocean-systems/chemical-sensor-group/floatviz/ ALTERNATE FORMATS: NetCDF and Matlab Matlab and NetCDF formatted files are provided for each ODV text file. The Matlab format is loaded as structure, FloatViz, with the ODV parameter names as the structure's fieldnames. The NetCDF format is similar to ARGO Float NetCDF format in its structure. The parameter names and flagging, however, match the ODV text parameter names. In addition to the quality control flag string entries, a numeric array of quality control flags is provided in the NetCDF files for programming convenience. Additionally, note that an explanation of Quality Flag Identifiers is included in each alternate format file. QUALITY CONTROL DOCUMENTATION: Delayed-mode quality control (DMQC) of biogeochemical float data within this archive is performed routinely by data managers at MBARI following Maurer et al (2021), https://doi.org/10.3389/fmars.2021.683207. QC notification emails are currently being sent out periodically to inform users of key updates to processing, QC and/or sensor calibrations for specific floats. All QC emails as of the date of this snapshot are included in each downloadable zip file. PARAMETERS: For information pertaining to float identification, sensor arrays, data parameters, and quality control please refer to descriptions within the file headers. Each snapshot within this collection includes estimated total alkalinity and derived carbon parameters for DIC and pCO2 using one of three algorithms (LIAR or CANYONB or ESPER). Estimated total alkalinity and derived carbon parameters from the ESPER algorithm are new additions to the standard snapshot collection as of December 2025. It is anticipated that ESPER will replace LIAR estimated total alkalinity and derived carbon parameters in future snapshot collection releases. Floats without a pH sensor will not have these additional parameters within their respective data files. See file headers for details. Additionally, files located at the urls listed above will include carbon parameters derived using observed pH and total alkalinity estimated by the LIAR method. All carbonate system variables calculated with CO2SYS for Matlab (Sharp et al., 2020; see also Lewis and Wallace 1998) used the following conditions: pH was reported on the total scale. K1 and K2 dissociation constants were from Lueker et al., 2000, doi:10.1016/S0304-4203(00)00022-0. The KSO4 dissociation constant was from Dickson, 1990, doi: 10.1016/0021-9614(90)90074-Z. The KF dissociation constant was from Perez and Fraga 1987, doi: 10.1016/0304-4203(87)90036-3. The borate to salinity ratio was from Lee et al., 2010, doi:10.1016/j.gca.2009.12.027. Silicate and Phosphate were not measured by the float, but estimates based on Redfieldian ratios improved the carbonate system estimates. If a nitrate value was considered to be of good quality silicate = nitrate*2.5 and phosphate = nitrate/16, otherwise the best estimate for both was considered to be 0. When pCO2 was estimated from TALK_LIAR (or TALK_ESPER) and pHinsitu, a bias was first added to pH (25C,0dbar) following Williams et al., 2017, doi: https:doi.org/10.1002/2016GB005541 , section 3.4, equation 3. This correction is not necessary for DIC and DIC is computed with the reported pH and the TALK_LIAR (or TALK_ESPER) value. RESOLUTION: This archive contains both low resolution and high resolution data. The format is defined by the folder name: SOCCOM_GO-BGC_LoResQC_METHOD_ddmmmyyyy or SOCCOM_GO-BGC_HiResQC_METHOD_ddmmmyyyy (where METHOD = LIAR or CANYONB or ESPER). Note that for APEX floats, the low resolution files only report data at depths where biogeochemical sensors sample, while the high resolution files merge this low resolution data with higher resolution pressure, temperature and salinity data (sampled every two meters in the upper 1000 meters). Be aware that, due to the merging of the two separate sampling schemes by interleaving the LowRes samples into the HiRes sample structure, HiRes files could potentially contain separate sets of samples with duplicate pressure values. For Navis floats all biogeochemical sensors except nitrate are sampled every 2 meters in the upper 1000 m. Additionally, all Navis float data is contained in both the LoRes and HiRes archives (per user request). DISCLAIMER: These data are provided as-is. We do our best to provide high-quality, complete data but make no guarantees as to the presence of errors within the data themselves or the algorithms used in the generation of derived parameters. It is the user's responsibility to ensure that the data meets the user's needs. However, please report any observed discrepancies in the data to the contact listed below and we will do our best to fix them. CONTACT: Please report any discrepancies, problems or concerns to the following and include "FLOATVIZ SNAPSHOT PROCESSING" in the subject line of the email. Tanya Maurer tmaurer@mbari.org Nicola Guisewhite nicolag@mbari.org SOCCOM/GO-BGC Data Management MBARI 7700 Sandholdt Road Moss Landing, CA 95039

  OA PDFDOI

• Cracking the Code: An Evidence-Based Approach to Teaching Python in an Undergraduate Earth Science Setting

  Abstracts with programs - Geological Society of America · 2025-01-01

  articleSenior author
  PublisherDOI

• Development of ambient noise measurement technique and its applications on Argo floats over the past two decades

  The Journal of the Acoustical Society of America · 2025-04-01

  article

  The distinctive underwater sound generated by raindrops on the ocean surface has been used to detect and quantify rainfall. Knowledge of the intensity and spatial–temporal distribution of rainfall over the ocean is critical in understanding the global hydrological cycle. However, rainfall is difficult to measure accurately over the ocean due to its spatial and temporal variability. To reduce these problems, satellite-based rain-monitoring instruments are used but they do not capture the full in situ temporal and spatial variability. The Passive Aquatic Listener (PAL) was developed at the University of Washington’s Applied Physics Laboratory (Nystuen, J. Acoust. Soc. 79, 92–98). PAL has been incorporated into Argo floats and deployed over global oceans. PAL-Argos are capable of telemetering back estimated rain rate and wind speed with a temporal resolution of 2–8 min, representing a circular surface footprint of a few kilometer radius (Yang et al., Oceanography 28, 124–133). In this work, the major operations of PAL-Argos in NASA’s Aquaris Satellite Mission, SPURS field efforts related to the Tropical Rainfall Measuring Mission, NOAA’s Tropical Pacific Observing System Initiative, and NSF’s Measurements and Modelling of the Indonesian Throughflow are chronicled with selective field data presented. [Work supported by NASA, NOAA, and NSF.]

  PublisherDOI

• Empirical ambient noise model based on wind speed using two-decade open ocean ambient noise data in the frequency band of 1–20 kHz

  The Journal of the Acoustical Society of America · 2025-04-01

  article

  In the frequency band of 1–20 kHz, wind-generated breaking surface waves produce bubbles near the surface that are the dominant ambient noise source. In previous work, two decades of ambient noise data from six deep ocean moorings were used to validate ambient noise models (Yang et al., JASA EL 3(3), 2023). Data-model comparisons show a mismatch, as existing models are monotonic in nature, i.e., the modeled spectral level increases with increasing wind speed for all frequencies, while data display a sharp drop-off that creates a “cross-over” as the spectral level for wind speed exceeding 15 m/s and frequency above ∼4 kHz becomes lower than that at lower wind speeds. This mismatch is due to attenuation when ambient sound propagates through the deeper and denser bubble layer under high sea conditions. In this work, an empirical ambient noise model utilizing wind speed only is presented as a baseline prediction with potential fine-tuning parameters such as bubble statistics, current and its direction, and wave height discussed. [Work supported by NOAA, NASA, and ONR.]

  PublisherDOI

• Cracking the code: An evidence-based approach to teaching Python in an undergraduate earth science setting

  2024-07-05 · 1 citations

  preprintOpen accessSenior author

  Scientific programming has become increasingly essential for manipulating, visualizing, and interpreting the large volumes of data acquired in earth science research. Yet few discipline-specific instructional approaches have been documented and assessed for their effectiveness in equipping geoscience undergraduate students with coding skills. Here we report on an evidence-based redesign of an introductory Python programming course, taught fully remotely in 2020 in the School of Oceanography at the University of Washington. Key components included a flipped structure, activities infused with active learning, an individualized final research project, and a focus on creating an accessible learning environment. Cloud-based notebooks were used to teach fundamental Python syntax as well as functions from packages widely used in climate-related disciplines. By analyzing quantitative and qualitative data from surveys, online learning platforms, student work, assessments, and a focus group, we conclude that the instructional design facilitated learning and supported self-guided scientific inquiry. Students with less or no prior exposure to coding achieved similar success as peers with more experience, an outcome likely mediated by higher engagement with course resources. We believe that the constructivist approach to teaching introductory programming and data literacy that we present could be broadly applicable across the earth sciences and in other scientific domains.

  PublisherDOI

• Global Estimates of Mesoscale Vertical Velocity Near 1,000 m From Argo Observations

  Journal of Geophysical Research Oceans · 2024-01-01 · 4 citations

  articleOpen accessSenior author

  Abstract Global estimates of mesoscale vertical velocity remain poorly constrained due to a historical lack of adequate observations on the spatial and temporal scales needed to measure these small magnitude velocities. However, with the wide‐spread and frequent observations collected by the Argo array of autonomous profiling floats, we can now better quantify mesoscale vertical velocities throughout the global ocean. We use the underutilized trajectory data files from the Argo array to estimate the time evolution of isotherm displacement around a float as it drifts at 1,000 m, allowing us to quantify vertical velocity averaged over approximately 4.5 days for that depth level. The resulting estimates have a non‐normal, high‐peak, and heavy‐tail distribution. The vertical velocity distribution has a mean value of (1.9 ± 0.02) × 10 −6 m s −1 and a median value of (1.3 ± 0.2) × 10 −7 m s −1 , but the high‐magnitude events can be up to the order of 10 −4 m s −1 . We find that vertical velocity is highly spatially variable and is largely associated with a combination of topographic features and horizontal flow. These are some of the first observational estimates of mesoscale vertical velocity to be taken across such large swaths of the ocean without assumptions of uniformity or reliance on horizontal divergence.

  PublisherOA PDFDOI

• The seasonal patterns of hydrographic and biogeochemical variables in the Ross Sea: A BGC-Argo analysis

  Deep Sea Research Part II Topical Studies in Oceanography · 2024-11-21 · 6 citations

  articleOpen access

  Seasonal patterns in seasonally frozen waters have usually been derived from composites of analyses conducted in different years and largely have been confined to ice-free periods. We present the first continuous measurements of hydrographic and biogeochemical variables collected over an entire year by Biogeochemical-Argo (BGC-Argo) profiling floats on the continental shelf of the Ross Sea. Analyses were divided into two periods: autumn/winter and spring/summer. Mixed layers increased rapidly upon ice cover, and nitrate, oxygen, and dissolved inorganic carbon vertical distributions were strongly influenced by this deeper mixing. Rates of nitrification in autumn were substantial and similar to rates measured in other areas of the ocean. Organic carbon disappearance was also most rapid in March. Changes in all variables slowed considerably after May. The largest mixed layer depths occurred at the southern floats and reached 400–500 m. Spring/summer patterns were similar to those observed during individual cruises, with rapid nitrate removal beginning in November, continuing through early January, but ceasing during austral summer. The most rapid accumulations of chlorophyll occurred prior to complete ice retreat. Substantial spatial differences were noted that were likely related to both mixed layer depths and phytoplankton composition. Particulate matter accumulated throughout the summer below 100 m, although the rates of change suggested substantial remineralization in the water column. The temporal patterns observed show the importance of relatively short periods that markedly influence the vertical distribution of biogeochemical parameters.

  PublisherDOI

• Sea ice-melt amount estimated from spring hydrography in the Sea of Okhotsk: spatial and interannual variabilities

  Journal of Oceanography · 2024-05-11 · 6 citations

  articleOpen accessSenior author

  Abstract This study provides the first estimation of sea ice-melt amount in the Sea of Okhotsk based on spring hydrographic data accumulated for nearly a hundred years. Just after sea ice melts completely, a low-salinity layer appears on the ocean surface, overlying the layer of Winter Water at the freezing point. The integration of the salinity decrease from Winter Water should correspond to the total ice-melt amount. We developed an algorithm to extract the profiles that clearly show the salinity deficit and converted the salinity deficit to the ice-melt amount from all available data. The climatological map shows that ice-melt amount decreases toward the ice edge and exhibits large values around the northern Sakhalin Island, reflecting the ice thickness distribution. In the southern area (south of 48°N), where sea ice is transported from the north, the average ice-melt amount is estimated to be ~ 71 cm in thickness. It is clearly shown that the ice-melt amount has decreased by ~ 30% in the southern area since the 1990s. These changes possibly affect the regional climate through the decreased latent heat of sea ice and potentially affect biological production through weakened stratification caused by decreased ice melt. We also suggested that ice-melt amount did not show a significant trend during the 1930s–1970s, implying that our methodology could extract information on sea ice before the era of satellite observations.

  PublisherOA PDFDOI

• Cracking the code: An evidence-based approach to teaching Python in an undergraduate earth science setting

  2024-01-29

  preprintOpen accessSenior author

  Scientific programming has become increasingly essential for manipulating, visualizing, and interpreting the large volumes of data acquired in earth science research. Yet few discipline-specific instructional approaches have been documented and assessed for their effectiveness in equipping geoscience undergraduate students with coding skills. Here we report on an evidence-based redesign of an introductory Python programming course, taught fully remotely in 2020 in the School of Oceanography at the University of Washington. Key components included a flipped structure, synchronous activities infused with active learning, an individualized final research project, and a focus on creating an accessible learning environment. Cloud-based notebooks were used to teach fundamental Python syntax as well as functions from packages widely used in climate-related disciplines. By analyzing quantitative and qualitative data from surveys, online learning platforms, student work, assessments, and a focus group, we conclude that the instructional design facilitated learning and supported self-guided scientific inquiry. Students with less or no prior exposure to coding achieved similar success to peers with more previous experience, an outcome likely mediated by higher engagement with course resources. We believe that the constructivist approach to teaching introductory programming and data literacy that we present could be broadly applicable across the earth sciences and in other scientific domains.

  PublisherDOI

• Evaluation of the Water Mass Composition in the Sea of Okhotsk and Its Long‐Term Change Using an Advanced Mapping Technique

  Journal of Geophysical Research Oceans · 2024-07-01 · 4 citations

  articleOpen accessSenior author

  Abstract The Sea of Okhotsk is a marginal sea that plays a major role in the ventilation of the North Pacific, being the key location where Dense Shelf Water (DSW) forms at the surface and sinks to the intermediate layer. The Okhotsk Sea Intermediate Water (OSIW) is a key water mass because it includes large amounts of DSW, outflows to the North Pacific, and supplies the ocean with the micronutrient iron. OSIW has been warming over the past few decades, which is attributed to a decreasing trend in DSW production. The acquisition of numerous hydrographic data after 2000 in the Kuril Basin, especially dissolved oxygen from profiling floats, offers an opportunity to better quantify the water mass composition of OSIW, and the changes in OSIW properties and DSW volume. Here, we used all available hydrographic records and a mapping technique specially adapted to polar and sub‐polar regions to revisit the Sea of Okhotsk water properties and document their long‐term changes. Our analysis revealed that the volume of heavier DSW (potential density above 26.9 kg.m −3 ) has decreased over the past three decades by 3,600 km 3 , or 15% of the volume present before 1990. This decline is nearly entirely compensated for by an increase in lighter DSW. This shift toward lighter DSW is possibly a sign of the weakening of the intermediate overturning circulation starting in the Okhotsk Sea. Additionally, we found that dense Soya Current Water only accounts for about 1% of OSIW, against the 5% previously estimated.

  PublisherOA PDFDOI

Recent grants

• Moored Observations of the Exchange between the North Pacific and the Okhotsk Sea through Bussol Strait

  NSF · $221k · 1998–2005

• Profiling Floats with Chemical Sensors for the Southern Ocean

  NSF · $298k · 2013–2015

• Collaborative Research: In situ measurements of oxygen and nitrate with profiling floats deployed at ocean time-series stations

  NSF · $932k · 2008–2012

• Collaborative Research: Observations and Models of Upper Ocean Water Mass Formation and Evolution in the Western North Atlantic

  NSF · $466k · 2000–2006

Frequent coauthors

• Kenneth S. Johnson

  Monterey Bay Aquarium Research Institute

  60 shared

• Lynne D. Talley

  Scripps Institution of Oceanography

  58 shared

• Jorge L. Sarmiento

  23 shared

• Alison R. Gray

  University of Washington

  21 shared

• Matthew R. Mazloff

  University of California, San Diego

  17 shared

• Nancy L. Williams

  17 shared

• J. L. Russell

  16 shared

• Emmanuel Boss

  15 shared

Labs

• OceanographyPI