the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Oceanographic Processes Favoring Deoxygenation Inside Patagonian Fjords
Pamela Linford
Iván Pérez-Santos
Paulina Montero
Patricio Díaz
Claudia Aracena
Elías Pinilla
Facundo Barrera
Manuel Castillo
Aida Alvera-Azcárate
Mónica Alvarado
Gabriel Soto
Cécile Pujol
Camila Schwerter
Sara Arenas-Uribe
Pilar Navarro
Guido Mancilla-Gutiérrez
Robinson Altamirano
Javiera San Martín
Camila Soto-Riquelme
Abstract. The dissolved oxygen (DO) levels of oceanic-coastal waters has decreased over the last decade owing to the increase in surface water temperature caused by climate change. In addition, biological and human activity in coastal zones, bays, and estuaries has contributed to the acceleration of current deoxygenation. The Patagonian fjord and channel system is one world region where low DO water (LDOW, 30 %–60 % oxygen saturation) and hypoxia conditions (< 30 % oxygen saturation, 2 ml L−1 or 89.2 µmol L−1) is observed. An in-situ data set of hydrographic and biogeochemical parameters (2017 stations), collected from sporadic oceanographic cruises between 1970 and 2021, was used to quantify the mechanism involved in the presence of LDOW and hypoxic conditions in northern Patagonian fjords. Results denoted two main areas with LDOW (e.g., Puyuhuapi Fjord-Jacaf channel, Comau Fjord, and the Reloncaví estuarine system) extending from 25–400 m depth. Simultaneously, hypoxia was recorded in the Puyuhuapi Fjord, Jacaf Channel, and Quitralco Fjord. Quitralco registered the lowest values of DO (9.36 µmol L−1 and 1.6 % oxygen saturation) of the entire Patagonian fjord system. Areas of LDOW and hypoxia coincided with the accumulation of inorganic nutrients. Water mass analysis confirmed the contribution of equatorial subsurface water in the advection of the LDOW to only the Puyuhuapi Fjord and Jacaf Channel. In addition, in Puyuhuapi Fjord, hypoxic conditions occurred when the community respiration rate (6.6 g C m−2d−1) exceeded the gross primary production estimate (1.9 g C m−2d−1) possibly due to the increased consumption of DO during the use of both autochthonous and allochthonous organic matter. Biogeochemical processes and circulation regimens also contribute to deoxygenation and will be part of the discussion of the present research.
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Pamela Linford et al.
Status: open (until 19 Jun 2023)
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CC1: 'Comment on egusphere-2023-706', Elin Darelius, 02 May 2023
reply
Dear Dr. Linford - thank you for an interesting paper! You include model results regarding the residence time. Are there any inducations / is it a possibility that changes in the residence time of the water within the fjords may have increased, and that this then would contribute to the decrease in oxygen consentrations? We have found this to be the case in Norwegian sill fjord, see e.g.
Darelius, E. (2020). On the effect of climate trends in coastal density on deep water renewal frequency in sill fjords—A statistical approach. Estuarine, Coastal and Shelf Science, 243. https://doi.org/10.1016/j.ecss.2020.106904
and
Aksnes, D. L., Aure, J., Johansen, P. O., Johnsen, G. H., & Salvanes, A. G. V. (2019). Multi-decadal warming of Atlantic water and associated decline of dissolved oxygen in a deep fjord. Estuarine, Coastal and Shelf Science, 228(September), 106392. https://doi.org/10.1016/j.ecss.2019.106392
Best regards, Elin
Citation: https://doi.org/10.5194/egusphere-2023-706-CC1 -
AC1: 'Reply on CC1', Iván Pérez-Santos, 02 May 2023
reply
Thank you for your interest in our paper and for bringing up the topic of changes in the residence time of water in fjords. We have indeed found indications of an increase in the residence time of water in our model results, as well as in other metrics such as water age. Our findings suggest that a decrease in river discharge can lead to slower circulation and longer residence times, which could contribute to the observed decrease in oxygen concentrations in fjords.
We appreciate you sharing the work of Darelius et al. (2020) and Aksnes et al. (2019) in Norwegian sill fjords, which further supports our findings. However, we acknowledge that our models currently cover only six years of data and do not yet extend to longer periods.
As such, we plan to extend our analysis to longer time periods in future research to better understand the long-term dynamics of fjord ecosystems and to identify any trends or patterns that may be obscured by short-term variations.
Thank you for your valuable contribution to this discussion, and we look forward to continuing to advance our understanding of fjord ecosystems.Citation: https://doi.org/10.5194/egusphere-2023-706-AC1
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AC1: 'Reply on CC1', Iván Pérez-Santos, 02 May 2023
reply
Pamela Linford et al.
Pamela Linford et al.
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