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

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Bach, LT and Paul, AJ and Boxhammer, T and von der Esch, E and Graco, M and Schulz, KG and Achterberg, E and Aguayo, P and Aristegui, J and Ayon, P and Banos, I and Bernales, A and Boegeholz, AS and Chavez, F and Chavez, G and Chen, S-M and Doering, K and Filella, A and Fischer, M and Grasse, P and Haunost, M and Hennke, J and Hernandez-Hernandez, N and Hopwood, M and Igarza, M and Kalter, V and Kittu, L and Kohnert, P and Ledesma, J and Lieberum, C and Lischka, S and Loscher, C and Ludwig, A and Mendoza, U and Meyer, J and Meyer, J and Minutolo, F and Ortiz Cortez, J and Piiparinen, J and Sforna, C and Spilling, K and Sanchez, S and Spisla, C and Sswat, M and Zavala Moreira, M and Riebesell, U, Factors controlling plankton community production, export flux, and particulate matter stoichiometry in the coastal upwelling system off Peru, Biogeosciences, 17 pp. 4831-4852. ISSN 1726-4170 (2020) [Refereed Article]


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Copyright 2020 The Authors. Licensed under Creative Commons Attribution 4.0 International (CC BY 4.0) https://creativecommons.org/licenses/by/4.0/

DOI: doi:10.5194/bg-17-4831-2020

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 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.

Item Details

Item Type:Refereed Article
Keywords:Eastern Boundary Upwelling System, Peru, production, phytoplankton, biological pump, stoichiometry
Research Division:Earth Sciences
Research Group:Oceanography
Research Field:Biological oceanography
Objective Division:Environmental Policy, Climate Change and Natural Hazards
Objective Group:Adaptation to climate change
Objective Field:Climate change adaptation measures (excl. ecosystem)
UTAS Author:Bach, LT (Dr Lennart Bach)
ID Code:141469
Year Published:2020
Web of Science® Times Cited:3
Deposited By:Ecology and Biodiversity
Deposited On:2020-10-22
Last Modified:2021-02-17
Downloads:3 View Download Statistics

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