BEGIN:VCALENDAR VERSION:2.0 X-WR-CALNAME:EventsCalendar PRODID:-//hacksw/handcal//NONSGML v1.0//EN CALSCALE:GREGORIAN BEGIN:VTIMEZONE TZID:America/New_York LAST-MODIFIED:20240422T053451Z TZURL:https://www.tzurl.org/zoneinfo-outlook/America/New_York X-LIC-LOCATION:America/New_York BEGIN:DAYLIGHT TZNAME:EDT TZOFFSETFROM:-0500 TZOFFSETTO:-0400 DTSTART:19700308T020000 RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU END:DAYLIGHT BEGIN:STANDARD TZNAME:EST TZOFFSETFROM:-0400 TZOFFSETTO:-0500 DTSTART:19701101T020000 RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU END:STANDARD END:VTIMEZONE BEGIN:VEVENT CATEGORIES:SMAST,SMAST Seminar Series DESCRIPTION:Department of Estuarine and Ocean Sciences"Autonomous measureme nt of denitrification in the open ocean" Dr. Mark AltabetProfessor and De partment Chair, Estuarine and Ocean Sciences, SMAST Wednesday, September 2 , 202612:30 - 1:30 pmSMAST E 101-103 and via Zoom Abstract: Denitrificatio n in oceanic oxygen-deficient zones (ODZs) removes a large but poorly cons trained fraction of the ocean's fixed nitrogen. The standard observational measure, the nitrogen deficit (Ndef), relies on chemical measurements of nitrate, nitrite, and phosphate. However, phosphate is not measured auto nomously, and the SUNA optical nitrate sensors carried by BGC-Argo floats have not routinely separated nitrate from the nitrite that accumulates in ODZ waters. We present an approach for estimating Ndef from autonomous pla tforms alone. Expected nitrate is reconstructed without phosphate, from al ong-isopycnal mixing between a fresh California Current source and a salty Eastern Equatorial Pacific source, with salinity and expected nitrate end members defined as functions of potential density. Nitrite is recovered fr om the same ultraviolet spectra and returned to the fixed-nitrogen total, correcting a potential overestimate of the deficit in ODZ waters. The meth od is validated in the Eastern Tropical North Pacific against three indepe ndent shipboard estimates — bottle nutrients, gas-tension N₂, and N₂ /Ar mass spectrometry — on two cruises. Agreement is within the propagat ed uncertainty of each method at essentially every station, and the gas-ph ase and nutrient-based deficits agree in the mean, supporting the Richards denitrification stoichiometry. A float time series is used to demonstrate variability of the Ndef on mesoscale time/space scales. Join Meeting http s://umassd.zoom.us/j/97440069270 Meeting ID and passcode required. Please email contact to obtain. For additional information, please contact Callie Rumbut at c.rumbut@umassd.edu\nEvent page: https://www.umassd.edu/events/ cms/9-2-26-autonomous-measurement-of-denitrification-in-the-open-ocean.php \nEvent link: https://umassd.zoom.us/j/97440069270 X-ALT-DESC;FMTTYPE=text/html:

Department of Estuarine and Oce an Sciences
"Autonomous measurement of denitrification in the open oc ean" Dr. Mark Altabet
Professor and Department Chair\, Estuarine and Ocean Sciences\, SMAST

Wednesday\, September 2\, 2026
12:30 - 1:30 pm
SMAST E 101-103 and via Zoom

Abstract:

Deni trification in oceanic oxygen-deficient zones (ODZs) removes a large but p oorly constrained fraction of the ocean's fixed nitrogen. The standard obs ervational measure\, the nitrogen deficit (Ndef)\, relies on chemical meas urements of nitrate\, nitrite\, and phosphate. However\, phosphate is no t measured autonomously\, and the SUNA optical nitrate sensors carried by BGC-Argo floats have not routinely separated nitrate from the nitrite that accumulates in ODZ waters.

We present an approach for estimating Ndef from autonomous platforms alone. Expected nitrate is reconstructed wi thout phosphate\, from along-isopycnal mixing between a fresh California C urrent source and a salty Eastern Equatorial Pacific source\, with salinit y and expected nitrate endmembers defined as functions of potential densit y. Nitrite is recovered from the same ultraviolet spectra and returned to the fixed-nitrogen total\, correcting a potential overestimate of the defi cit in ODZ waters.

The method is validated in the Eastern Tropical North Pacific against three independent shipboard estimates — bottle nu trients\, gas-tension N₂\, and N₂/Ar mass spectrometry — on two crui ses. Agreement is within the propagated uncertainty of each method at esse ntially every station\, and the gas-phase and nutrient-based deficits agre e in the mean\, supporting the Richards denitrification stoichiometry. A f loat time series is used to demonstrate variability of the Ndef on mesosca le time/space scales.

Join Meeting

https://umassd.zoom.us/ j/97440069270

Meeting ID and passcode required. Please email conta ct to obtain.

For additional information\, please contact Callie R umbut at c.rumbut@umassd.edu

Event page: https://www.umassd.edu/events/cms/9-2-26-autonomous-measurem ent-of-denitrification-in-the-open-ocean.php
Event link: https://umassd.zoom.us/j/97440069270< /a>

DTSTAMP:20260825T222741 DTSTART;TZID=America/New_York:20260902T123000 DTEND;TZID=America/New_York:20260902T133000 LOCATION:SMAST East 101-103 SUMMARY;LANGUAGE=en-us:"Autonomous measurement of denitrification in the op en ocean" by: Mark Altabet UID:a6ca1891a6e56f4ad899be70d0821b54@www.umassd.edu END:VEVENT END:VCALENDAR