The effect of nutrient supply ratios on organic matter dynamics, phytoplankton community composition and diazotrophy in the eastern tropical South Pacific.

Meyer, Judith, Lavik, Gaute and Riebesell, Ulf (2015) The effect of nutrient supply ratios on organic matter dynamics, phytoplankton community composition and diazotrophy in the eastern tropical South Pacific. [Poster] In: AGU Fall Meeting 2015. , 14.-18.12.2015, San Francisco, USA .

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Abstract

Upwelling of nutrient loaded water masses with low inorganic nitrogen (N) to phosphorus (P)
ratios is thought to favor non-Redfield primary production by phytoplankton species adapted
to exponential growth. Additionally, an excess of P (P*) in OMZ-influenced waters is also
supposed to provide a niche for nitrogen fixing organisms. In order to assess the influence of
low inorganic nutrient ratios on the stoichiometry and composition of primary producers,
biogeochemical measurements were carried out in the eastern tropical South Pacific during
R/V Meteor cruise M93. A succession of different functional types of phytoplankton was
observed along onshore – offshore transects with diatoms dominating the productive
upwelling region, while haptophytes, cryptophytes and crysophytes prevailed in the more
oligotrophic open ocean. Simultaneously, particulate organic nitrogen to phosphorus ratios
increased with increasing distance from shore. The stoichiometry of organic matter, however,
always exceeded ratios of 16:1, although nutrient supply ratios were below Redfield
proportions in the whole sampling area. A considerable amount of P* was detected in the
surface ocean layer above the shelf, which decreased as water masses were advected
beyond the shelf slope. Phytoplankton pigment analyses with HPLC revealed the existence
of diazotrophic marker pigments in the study area, hinting towards a local replenishment of
the N-deficit via nitrogen fixation.

Document Type: Conference or Workshop Item (Poster)
Keywords: nutrient stoichiometry, OMZ, phytoplankton composition, diazotrophs
Research affiliation: OceanRep > SFB 754 > B2
OceanRep > SFB 754 > B4
OceanRep > SFB 754
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BI Biological Oceanography
Projects: SFB754
Date Deposited: 27 Jan 2016 14:12
Last Modified: 27 Jan 2016 14:12
URI: http://oceanrep.geomar.de/id/eprint/31200

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