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| Titel |
Physical and biogeochemical forcing of oxygen and nitrate changes during El Niño/El Viejo and La Niña/La Vieja upper-ocean phases in the tropical eastern South Pacific along 86° W |
| VerfasserIn |
P. J. Llanillo, J. Karstensen, J. L. Pelegrí, L. Stramma |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 10 ; Nr. 10, no. 10 (2013-10-09), S.6339-6355 |
| Datensatznummer |
250085353
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| Publikation (Nr.) |
 copernicus.org/bg-10-6339-2013.pdf |
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| Zusammenfassung |
| Temporal changes in the water mass distribution and biogeochemical signals in
the tropical eastern South Pacific are investigated with the help of an
extended optimum multi-parameter (OMP) analysis, a technique for inverse
modeling of mixing and biogeochemical processes through a multidimensional
least-square fit. Two ship occupations of a meridional section along
85°50' W from 14° S to 1° N are analysed during
relatively warm (El Niño/El Viejo, March 1993) and cold (La Niña/La
Vieja, February 2009) upper-ocean phases. The largest El Niño–Southern
Oscillation (ENSO) impact was found in the water properties and water mass
distribution in the upper 200 m north of 10° S. ENSO promotes the
vertical motion of the oxygen minimum zone (OMZ) associated with the hypoxic
equatorial subsurface water (ESSW). During a cold phase the core of the ESSW
is found at shallower layers, replacing shallow (top 200 m) subtropical
surface water (STW). The heave of isopycnals due to ENSO partially explains
the intrusion of oxygen-rich and nutrient-poor antarctic intermediate water
(AAIW) into the depth range of 150–500 m. The other cause of the AAIW
increase at shallower depths is that this water mass flowed along shallower
isopycnals in 2009. The shift in the vertical location of AAIW reaching the
OMZ induces changes in the amount of oxygen advected and respired inside the
OMZ: the larger the oxygen supply, the greater the respiration and the lower
the nitrate loss through denitrification. Variations in the intensity of the
zonal currents in the equatorial current system, which ventilates the OMZ
from the west, are used to explain the patchy latitudinal changes of seawater
properties observed along the repeated section. Significant changes reach
down to 800 m, suggesting that decadal variability (Pacific decadal
oscillation) is also a potential driver in the observed variability. |
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