Tracer-based assessment of the origin and biogeochemical transformation of a cyclonic eddy in the Sargasso Sea

Qian P. Li, Dennis A Hansell, Dennis J. McGillicuddy, Nicholas R. Bates, Rodney J. Johnson

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

Mechanisms of nutrient supply in oligotrophic ocean systems remain inadequately understood and quantified. In the North Atlantic Subtropical Gyre, for example, the observed rates of new production are apparently not balanced by nutrient supply via vertical mixing. Mesoscale eddies have been hypothesized as a mechanism for vertical nutrient pumping into the euphotic zone, but the full range and magnitude of biogeochemical impacts by eddies remain uncertain. We evaluated a cyclonic eddy located near Bermuda for its effect on water column biogeochemistry. In the density range σθ 26.1 to 26.7, an eddy core with anomalous salinity, temperature, and biogeochemical properties was observed, suggesting that the eddy was not formed with local water (i.e., not formed of the waters surrounding the eddy at the time of observations), hence complicating efforts to quantify biogeochemical processes in the eddy. We combined conservative hydrographic tracers (density versus potential temperature and salinity) and quasi-conservative biogeochemical tracers (density versus NO, PO, and total organic carbon) to propose the origin of the eddy core water to have been several hundred kilometers to the southeast of the eddy location at sampling. By comparing the observed eddy core's biogeochemical properties with those near the proposed origin, we estimate the net changes in biogeochemical properties that occurred. A conservative estimate of export was 0.5 ± 0.34 mol N m-2 via sinking particles, with export occurring prior to our period of direct observation. Our results suggest that biogeochemical signals induced by mesoscale eddies could survive to be transported over long distances, thus providing a mechanism for lateral fluxes of nutrients and AOU (apparent oxygen utilization). Given that the proposed source area of this eddy is relatively broad, and the eddy-mixing history before our sampling is unknown, uncertainty remains in our assessment of the true biogeochemical impact of mesoscale eddies in the gyre.

Original languageEnglish (US)
Article numberC10006
JournalJournal of Geophysical Research C: Oceans
Volume113
Issue number10
DOIs
StatePublished - Oct 8 2008

Fingerprint

Sargasso Sea
Nutrients
tracers
eddy
tracer
vortices
Water
Biogeochemistry
Sampling
mesoscale eddy
nutrients
Organic carbon
nutrient
gyre
Oxygen
Fluxes
Temperature
salinity
sea
water

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Oceanography

Cite this

Tracer-based assessment of the origin and biogeochemical transformation of a cyclonic eddy in the Sargasso Sea. / Li, Qian P.; Hansell, Dennis A; McGillicuddy, Dennis J.; Bates, Nicholas R.; Johnson, Rodney J.

In: Journal of Geophysical Research C: Oceans, Vol. 113, No. 10, C10006, 08.10.2008.

Research output: Contribution to journalArticle

Li, Qian P. ; Hansell, Dennis A ; McGillicuddy, Dennis J. ; Bates, Nicholas R. ; Johnson, Rodney J. / Tracer-based assessment of the origin and biogeochemical transformation of a cyclonic eddy in the Sargasso Sea. In: Journal of Geophysical Research C: Oceans. 2008 ; Vol. 113, No. 10.
@article{07d2d64af61d4f4dadf1ab21ffa3cebd,
title = "Tracer-based assessment of the origin and biogeochemical transformation of a cyclonic eddy in the Sargasso Sea",
abstract = "Mechanisms of nutrient supply in oligotrophic ocean systems remain inadequately understood and quantified. In the North Atlantic Subtropical Gyre, for example, the observed rates of new production are apparently not balanced by nutrient supply via vertical mixing. Mesoscale eddies have been hypothesized as a mechanism for vertical nutrient pumping into the euphotic zone, but the full range and magnitude of biogeochemical impacts by eddies remain uncertain. We evaluated a cyclonic eddy located near Bermuda for its effect on water column biogeochemistry. In the density range σθ 26.1 to 26.7, an eddy core with anomalous salinity, temperature, and biogeochemical properties was observed, suggesting that the eddy was not formed with local water (i.e., not formed of the waters surrounding the eddy at the time of observations), hence complicating efforts to quantify biogeochemical processes in the eddy. We combined conservative hydrographic tracers (density versus potential temperature and salinity) and quasi-conservative biogeochemical tracers (density versus NO, PO, and total organic carbon) to propose the origin of the eddy core water to have been several hundred kilometers to the southeast of the eddy location at sampling. By comparing the observed eddy core's biogeochemical properties with those near the proposed origin, we estimate the net changes in biogeochemical properties that occurred. A conservative estimate of export was 0.5 ± 0.34 mol N m-2 via sinking particles, with export occurring prior to our period of direct observation. Our results suggest that biogeochemical signals induced by mesoscale eddies could survive to be transported over long distances, thus providing a mechanism for lateral fluxes of nutrients and AOU (apparent oxygen utilization). Given that the proposed source area of this eddy is relatively broad, and the eddy-mixing history before our sampling is unknown, uncertainty remains in our assessment of the true biogeochemical impact of mesoscale eddies in the gyre.",
author = "Li, {Qian P.} and Hansell, {Dennis A} and McGillicuddy, {Dennis J.} and Bates, {Nicholas R.} and Johnson, {Rodney J.}",
year = "2008",
month = "10",
day = "8",
doi = "10.1029/2008JC004840",
language = "English (US)",
volume = "113",
journal = "Journal of Geophysical Research: Oceans",
issn = "2169-9275",
publisher = "Wiley-Blackwell",
number = "10",

}

TY - JOUR

T1 - Tracer-based assessment of the origin and biogeochemical transformation of a cyclonic eddy in the Sargasso Sea

AU - Li, Qian P.

AU - Hansell, Dennis A

AU - McGillicuddy, Dennis J.

AU - Bates, Nicholas R.

AU - Johnson, Rodney J.

PY - 2008/10/8

Y1 - 2008/10/8

N2 - Mechanisms of nutrient supply in oligotrophic ocean systems remain inadequately understood and quantified. In the North Atlantic Subtropical Gyre, for example, the observed rates of new production are apparently not balanced by nutrient supply via vertical mixing. Mesoscale eddies have been hypothesized as a mechanism for vertical nutrient pumping into the euphotic zone, but the full range and magnitude of biogeochemical impacts by eddies remain uncertain. We evaluated a cyclonic eddy located near Bermuda for its effect on water column biogeochemistry. In the density range σθ 26.1 to 26.7, an eddy core with anomalous salinity, temperature, and biogeochemical properties was observed, suggesting that the eddy was not formed with local water (i.e., not formed of the waters surrounding the eddy at the time of observations), hence complicating efforts to quantify biogeochemical processes in the eddy. We combined conservative hydrographic tracers (density versus potential temperature and salinity) and quasi-conservative biogeochemical tracers (density versus NO, PO, and total organic carbon) to propose the origin of the eddy core water to have been several hundred kilometers to the southeast of the eddy location at sampling. By comparing the observed eddy core's biogeochemical properties with those near the proposed origin, we estimate the net changes in biogeochemical properties that occurred. A conservative estimate of export was 0.5 ± 0.34 mol N m-2 via sinking particles, with export occurring prior to our period of direct observation. Our results suggest that biogeochemical signals induced by mesoscale eddies could survive to be transported over long distances, thus providing a mechanism for lateral fluxes of nutrients and AOU (apparent oxygen utilization). Given that the proposed source area of this eddy is relatively broad, and the eddy-mixing history before our sampling is unknown, uncertainty remains in our assessment of the true biogeochemical impact of mesoscale eddies in the gyre.

AB - Mechanisms of nutrient supply in oligotrophic ocean systems remain inadequately understood and quantified. In the North Atlantic Subtropical Gyre, for example, the observed rates of new production are apparently not balanced by nutrient supply via vertical mixing. Mesoscale eddies have been hypothesized as a mechanism for vertical nutrient pumping into the euphotic zone, but the full range and magnitude of biogeochemical impacts by eddies remain uncertain. We evaluated a cyclonic eddy located near Bermuda for its effect on water column biogeochemistry. In the density range σθ 26.1 to 26.7, an eddy core with anomalous salinity, temperature, and biogeochemical properties was observed, suggesting that the eddy was not formed with local water (i.e., not formed of the waters surrounding the eddy at the time of observations), hence complicating efforts to quantify biogeochemical processes in the eddy. We combined conservative hydrographic tracers (density versus potential temperature and salinity) and quasi-conservative biogeochemical tracers (density versus NO, PO, and total organic carbon) to propose the origin of the eddy core water to have been several hundred kilometers to the southeast of the eddy location at sampling. By comparing the observed eddy core's biogeochemical properties with those near the proposed origin, we estimate the net changes in biogeochemical properties that occurred. A conservative estimate of export was 0.5 ± 0.34 mol N m-2 via sinking particles, with export occurring prior to our period of direct observation. Our results suggest that biogeochemical signals induced by mesoscale eddies could survive to be transported over long distances, thus providing a mechanism for lateral fluxes of nutrients and AOU (apparent oxygen utilization). Given that the proposed source area of this eddy is relatively broad, and the eddy-mixing history before our sampling is unknown, uncertainty remains in our assessment of the true biogeochemical impact of mesoscale eddies in the gyre.

UR - http://www.scopus.com/inward/record.url?scp=57549111813&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=57549111813&partnerID=8YFLogxK

U2 - 10.1029/2008JC004840

DO - 10.1029/2008JC004840

M3 - Article

VL - 113

JO - Journal of Geophysical Research: Oceans

JF - Journal of Geophysical Research: Oceans

SN - 2169-9275

IS - 10

M1 - C10006

ER -