B.
Sabbaghzadeh1, D. L.
Arévalo-Martínez2*, V. Mohrholz1, L.
C. Cotovicz Jr.1, S. Otto1, G.
Dangl1, M. Glockzin1, and G.
Rehder1
1 Leibniz Institute for Baltic Sea Research
Warnemünde, Rostock, Germany, 2 GEOMAR Helmholtz
Centre for Ocean Research Kiel, Germany, * current address: Radboud
University Nijmegen, Netherlands
Correspondence to: B. Sabbaghzadeh, bita.sabbaghzadeh@io-warnemuende.de
B.Sabbaghzadeh ORCID NO: 0000-0002-1232-0576
Key Points:
- The northern Benguela Upwelling System is a perennial source of
long-lived greenhouse gases due to upwelling-driven winter peaks.
- Seasonal water column variations show rising pCO2, N2O and
CH4 from winter to summer, confined to the inner
shelf.
- It is imperative to consider non-CO2 greenhouse gases
when assessing the far-reaching impacts of coastal waters on climate
change.
Abstract
The northern Benguela Upwelling System (nBUS) represents one of the
ocean’s largest and most biologically productive marine ecosystems,
crucial for the cycling of greenhouse gases (GHG). Despite its
significance, there is a scarcity of direct evidence on the seasonal
variability of GHG production and emissions in the nBUS and its major
driving factors. Through multi-year observations, we examined the
spatio-temporal dynamics in the nBUS to understand their influence on
GHG dynamics. Our findings revealed coastal GHG hotspots with seasonal
gradients, primarily influenced by upwelling. The nBUS consistently
acted as a perennial source of GHG to the atmosphere, with peak
CO2, CH4, and N2O
sea-air fluxes during austral winter (increases of 97%, 47%, and 87%
compared to austral summer, respectively). Winter
CO2-equivalent (CO2-e) emissions
accounted for 70 – 73% of GHG emissions, followed by
N2O (23 – 24%) and CH4 (2 – 6%). In
summer, these percentages shifted considerably, with CO2 contributing 23 – 30%, N2O 38 – 51%, and
CH4 17 – 38%. We argue for the necessity of including
non-CO2 GHG when assessing the impacts of coastal
ecosystems on climate dynamics. Our results offer detailed insights into
the primary drivers of spatial and seasonal variability in GHG dynamics
within coastal upwelling waters. This study constitutes the first
comprehensive simultaneously evaluation of all three GHG within the
region. It serves as a foundational framework for subsequent model
studies aimed at refining the sea-air flux variability, particularly in
anticipation of projected ocean warming and the expanding oxygen minimum
zones.