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Particle production and transformation in the Eastern Tropical North Pacific Oxygen Deficient Zone: a δ15N-amino acids’ perspective
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  • Charlotte Wing Man Lee,
  • Mark A Altabet,
  • Alanna M Mnich,
  • Lin Zhang
Charlotte Wing Man Lee
Texas A&M University - Corpus Christi
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Mark A Altabet
University of Massachusetts Dartmouth
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Alanna M Mnich
University of Massachusetts Dartmouth
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Lin Zhang
Texus A&M Univeristy-Corpus Christi

Corresponding Author:[email protected]

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Abstract

The eastern tropical North Pacific oxygen deficient zone (ETNP-ODZ) exhibits a distinct physical and biological environment compared to other oxygenated water columns, leading to a unique scenario of particulate organic matter (POM) production and vertical transport. To elucidate these biological pump processes, we present the first comparison of δ¹⁵N values of nitrate, phenylalanine (Phe), and glutamic acid (Glu) within two distinct size fractions of particles collected along a productivity gradient in the ETNP-ODZ. Low δ¹⁵NPhe and δ¹⁵NGlu values in both particle pools at the secondary chlorophyll maximum (SCM), compared to the ambient δ¹⁵N-NO₃-, suggest the presence of recycled N-utilizing primary producers distinct from those at the primary chlorophyll maximum and their contribution to export. We observed reduced ¹⁵N enrichment of Phe in suspended particles and a narrower δ¹⁵NPhe disparity between the two particle size fractions compared to the results from oxic waters, likely due to slower microbial remineralization of suspended particles. Unique δ¹⁵NPhe and δ¹⁵NGlu signatures of particles were found at the lower oxycline, potentially attributable to chemoautotrophic production and zooplankton mediation. These findings underscore the need for further investigations targeting particles generated at the SCM, their subsequent alteration by zooplankton, and the new production by chemoautotrophs. This will allow for a better evaluation of the efficiency of the biological pump in the expanding ODZs.
09 Jul 2024Submitted to ESS Open Archive
11 Jul 2024Published in ESS Open Archive