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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-91
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-91
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 21 Mar 2019

Submitted as: research article | 21 Mar 2019

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Biogeosciences (BG).

The influence of decadal oscillations on the oxygen and nutrient trends in the Pacific Ocean

Lothar Stramma1, Sunke Schmidtko1, Steven J. Bograd2, Tsuneo Ono3, Tetjana Ross4, Daisuke Sasano5, and Frank A. Whitney4 Lothar Stramma et al.
  • 1GEOMAR Helmholtz Centre for Ocean Research 5 Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany
  • 2Environmental Research Division, Southwest Fisheries Science Center, NOAA, Monterey, California, USA
  • 3National Research Institute for Far Sea Fisheries, Fisheries Research and Education Agency, 2-12-4 Fukuura, Kanazawa-Ku, Yokohama 236-8648, Japan
  • 4Institute of Ocean Sciences, Fisheries and Oceans Canada, PO Box 6000, Sidney BC V8L 4B2, Canada
  • 5Global Environment and Marine Department, Japan Meteorological Agency, Tokyo, Japan

Abstract. A strong oxygen deficient layer is located in the upper layer of the tropical Pacific Ocean and at deeper depths in the North Pacific. Processes related to climate change (upper ocean warming, reduced ventilation) are expected to change ocean oxygen and nutrient inventories. In most ocean basins, a decrease in oxygen (‘deoxygenation’) and an increase of nutrients has been observed in subsurface layers. Deoxygenation trends are not linear and there could be other influences on oxygen and nutrient trends and variability. Here oxygen and nutrient time series since 1950 in the Pacific Ocean were investigated at 50 to 300 m depth, as this layer provides critical pelagic habitat for biological communities. In addition to trends related to ocean warming the oxygen and nutrient trends show a strong influence of the Pacific Decadal Oscillation (PDO) in the tropical and the eastern Pacific, and the North Pacific Gyre Oscillation (NPGO) especially in the North Pacific. In the Oyashio Region the PDO, the NPGO, the North Pacific Index (NPI) and a 18.6 year nodal tidal cycle overlay the long-term trend. In most regions oxygen increases and nutrients decrease in the 50 to 300 m layer during the negative PDO phase, with opposite trends during the positive PDO phase. The PDO index encapsulates the major mode of surface temperature variability in the Pacific and oxygen and nutrients trends throughout the basin can be described in the context of the PDO phases. An influence of the subtropical-tropical cell in the tropical Pacific cannot be proven with the available data. El Niño and La Niña years often influence the oxygen and nutrient distribution during the event in the eastern tropical Pacific, but do not have a multi-year influence on the trends.

Lothar Stramma et al.
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Lothar Stramma et al.
Lothar Stramma et al.
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Short summary
The influence of climate signals in the Pacific especially the Pacific Decadal Oscillation and the North Pacific Gyre Oscillation as well as the El Nino/La Nina and a 18.6 year nodal tidal cycle on oxygen and nutrient trends is investigated. At different locations in the Pacific Ocean different climate signals dominate. Hence, not only trends related to warming but also the influence of climate signals needs to be investigated to understand oxygen and nutrient changes in the Ocean.
The influence of climate signals in the Pacific especially the Pacific Decadal Oscillation and...
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