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Factors controlling plankton community production, export flux, and particulate matter stoichiometry in the coastal upwelling system off Peru

Bach, Lennart Thomas ; Paul, Allanah Joy ; Boxhammer, Tim ; von der Esch, Elisabeth ; Graco, Michelle ; Schulz, Kai Georg ; Achterberg, Eric ; Aguayo, Paulina ; Arístegui, Javier and Ayón, Patrizia , et al. (2020) In Biogeosciences 17(19). p.4831-4852
Abstract

Eastern boundary upwelling systems (EBUS) are among the most productive marine ecosystems on Earth. The production of organic material is fueled by upwelling of nutrient-rich deep waters and high incident light at the sea surface. However, biotic and abiotic factors can modify surface production and related biogeochemical processes. Determining these factors is important because EBUS are considered hotspots of climate change, and reliable predictions of their future functioning requires understanding of the mechanisms driving the biogeochemical cycles therein. In this field experiment, we used in situ mesocosms as tools to improve our mechanistic understanding of processes controlling organic matter cycling in the coastal Peruvian... (More)

Eastern boundary upwelling systems (EBUS) are among the most productive marine ecosystems on Earth. The production of organic material is fueled by upwelling of nutrient-rich deep waters and high incident light at the sea surface. However, biotic and abiotic factors can modify surface production and related biogeochemical processes. Determining these factors is important because EBUS are considered hotspots of climate change, and reliable predictions of their future functioning requires understanding of the mechanisms driving the biogeochemical cycles therein. In this field experiment, we used in situ mesocosms as tools to improve our mechanistic understanding of processes controlling organic matter cycling in the coastal Peruvian upwelling system. Eight mesocosms, each with a volume of ∼ 55 m3, were deployed for 50 d ∼ 6 km off Callao (12◦ S) during austral summer 2017, coinciding with a coastal El Niño phase. After mesocosm deployment, we collected subsurface waters at two different locations in the regional oxygen minimum zone (OMZ) and injected these into four mesocosms (mixing ratio ≈ 1.5: 1 mesocosm: OMZ water). The focus of this paper is on temporal developments of organic matter production, export, and stoichiometry in the individual mesocosms. The mesocosm phytoplankton communities were initially dominated by diatoms but shifted towards a pronounced dominance of the mixotrophic dinoflagellate (Akashiwo sanguinea) when inorganic nitrogen was exhausted in surface layers. The community shift coincided with a short-term increase in production during the A. sanguinea bloom, which left a pronounced imprint on organic matter C: N: P stoichiometry. However, C, N, and P export fluxes did not increase because A. sanguinea persisted in the water column and did not sink out during the experiment. Accordingly, export fluxes during the study were decoupled from surface production and sustained by the remaining plankton community. Overall, biogeochemical pools and fluxes were surprisingly constant for most of the experiment. We explain this constancy by light limitation through self-shading by phytoplankton and by inorganic nitrogen limitation which constrained phytoplankton growth. Thus, gain and loss processes remained balanced and there were few opportunities for blooms, which represents an event where the system becomes unbalanced. Overall, our mesocosm study revealed some key links between ecological and biogeochemical processes for one of the most economically important regions in the oceans.

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type
Contribution to journal
publication status
published
subject
in
Biogeosciences
volume
17
issue
19
pages
22 pages
publisher
Copernicus GmbH
external identifiers
  • scopus:85092769280
ISSN
1726-4170
DOI
10.5194/bg-17-4831-2020
language
English
LU publication?
no
additional info
Funding Information: Financial support. This research has been supported by the Collaborative Research Center SFB 754 Climate-Biogeochemistry Interactions in the Tropical Ocean financed by the German Research Foundation (DFG), the EU project AQUACOSM, and the Leibniz Award 2012 (granted to Ulf Riebesell). Funding Information: Acknowledgements. We thank all participants of the KOSMOS Peru 2017 study for assisting in mesocosm sampling and maintenance. We are particularly thankful to the staff of IMARPE for their support during the planning, preparation, and execution of this study and to the captains and crews of BAP Morales, IMARPE VI, and BIC Humboldt for support during deployment and recovery of the mesocosms and various operations during the course of this investigation. Special thanks go to the Marina de Guerra del Perú, in particular the submarine section of the navy of Callao, and to the Direc-ción General de Capitanías y Guardacostas. We also acknowledge strong support for sampling and mesocosm maintenance by Jean-Pierre Bednar, Susanne Feiersinger, Peter Fritsche, Paul Stange, Anna Schukat, and Michael Krudewig. We want to thank Club Náu-tico Del Centro Naval for excellent hosting of our temporary filtration laboratory and office space and their great support and improvisation skills after two of our boats were lost. This work is a contribution in the framework of the cooperation agreement between IMARPE and GEOMAR through the German Federal Ministry of Education and Research (BMBF) project ASLAEL 12-016 and the national project Integrated Study of the Upwelling System off Peru developed by the Directorate of Oceanography and Climate Change of IMARPE, PPR 137 CONCYTEC. Publisher Copyright: © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License.
id
feb5ac60-0691-455b-96c1-6ea732ae38d6
date added to LUP
2022-09-05 12:37:57
date last changed
2022-09-15 21:39:18
@article{feb5ac60-0691-455b-96c1-6ea732ae38d6,
  abstract     = {{<p>Eastern boundary upwelling systems (EBUS) are among the most productive marine ecosystems on Earth. The production of organic material is fueled by upwelling of nutrient-rich deep waters and high incident light at the sea surface. However, biotic and abiotic factors can modify surface production and related biogeochemical processes. Determining these factors is important because EBUS are considered hotspots of climate change, and reliable predictions of their future functioning requires understanding of the mechanisms driving the biogeochemical cycles therein. In this field experiment, we used in situ mesocosms as tools to improve our mechanistic understanding of processes controlling organic matter cycling in the coastal Peruvian upwelling system. Eight mesocosms, each with a volume of ∼ 55 m<sup>3</sup>, were deployed for 50 d ∼ 6 km off Callao (12<sup>◦</sup> S) during austral summer 2017, coinciding with a coastal El Niño phase. After mesocosm deployment, we collected subsurface waters at two different locations in the regional oxygen minimum zone (OMZ) and injected these into four mesocosms (mixing ratio ≈ 1.5: 1 mesocosm: OMZ water). The focus of this paper is on temporal developments of organic matter production, export, and stoichiometry in the individual mesocosms. The mesocosm phytoplankton communities were initially dominated by diatoms but shifted towards a pronounced dominance of the mixotrophic dinoflagellate (Akashiwo sanguinea) when inorganic nitrogen was exhausted in surface layers. The community shift coincided with a short-term increase in production during the A. sanguinea bloom, which left a pronounced imprint on organic matter C: N: P stoichiometry. However, C, N, and P export fluxes did not increase because A. sanguinea persisted in the water column and did not sink out during the experiment. Accordingly, export fluxes during the study were decoupled from surface production and sustained by the remaining plankton community. Overall, biogeochemical pools and fluxes were surprisingly constant for most of the experiment. We explain this constancy by light limitation through self-shading by phytoplankton and by inorganic nitrogen limitation which constrained phytoplankton growth. Thus, gain and loss processes remained balanced and there were few opportunities for blooms, which represents an event where the system becomes unbalanced. Overall, our mesocosm study revealed some key links between ecological and biogeochemical processes for one of the most economically important regions in the oceans.</p>}},
  author       = {{Bach, Lennart Thomas and Paul, Allanah Joy and Boxhammer, Tim and von der Esch, Elisabeth and Graco, Michelle and Schulz, Kai Georg and Achterberg, Eric and Aguayo, Paulina and Arístegui, Javier and Ayón, Patrizia and Baños, Isabel and Bernales, Avy and Boegeholz, Anne Sophie and Chavez, Francisco and Chavez, Gabriela and Chen, Shao Min and Doering, Kristin and Filella, Alba and Fischer, Martin and Grasse, Patricia and Haunost, Mathias and Hennke, Jan and Hernández-Hernández, Nauzet and Hopwood, Mark and Igarza, Maricarmen and Kalter, Verena and Kittu, Leila and Kohnert, Peter and Ledesma, Jesus and Lieberum, Christian and Lischka, Silke and Löscher, Carolin and Ludwig, Andrea and Mendoza, Ursula and Meyer, Jana and Meyer, Judith and Minutolo, Fabrizio and Cortes, Joaquin Ortiz and Piiparinen, Jonna and Sforna, Claudia and Spilling, Kristian and Sanchez, Sonia and Spisla, Carsten and Sswat, Michael and Moreira, Mabel Zavala and Riebesell, Ulf}},
  issn         = {{1726-4170}},
  language     = {{eng}},
  month        = {{10}},
  number       = {{19}},
  pages        = {{4831--4852}},
  publisher    = {{Copernicus GmbH}},
  series       = {{Biogeosciences}},
  title        = {{Factors controlling plankton community production, export flux, and particulate matter stoichiometry in the coastal upwelling system off Peru}},
  url          = {{http://dx.doi.org/10.5194/bg-17-4831-2020}},
  doi          = {{10.5194/bg-17-4831-2020}},
  volume       = {{17}},
  year         = {{2020}},
}