Spatiotemporal variations in surface marine carbonate system properties across the western Mediterranean Sea using volunteer observing ship data
<p>Surface physical and marine carbonate system (MCS) properties were assessed along the western boundary of the Mediterranean Sea. An unprecedented high-resolution observation-based dataset spanning 5 years (2019–2024) was built through automatic underway monitoring by a volunteer observing s...
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| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-07-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/22/3329/2025/bg-22-3329-2025.pdf |
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| Summary: | <p>Surface physical and marine carbonate system (MCS) properties were assessed along the western boundary of the Mediterranean Sea. An unprecedented high-resolution observation-based dataset spanning 5 years (2019–2024) was built through automatic underway monitoring by a volunteer observing ship (VOS). The MCS dynamics were strongly modulated by physical–biological coupling dependent on the upper-layer circulation and mesoscale features. The variations in CO<span class="inline-formula"><sub>2</sub></span> fugacity (<span class="inline-formula"><i>f</i></span>CO<span class="inline-formula"><sub>2,sw</sub></span>) were mainly driven by sea surface temperature (SST) changes. On a seasonal scale, SST explained 51 %–71 % of the increase in <span class="inline-formula"><i>f</i></span>CO<span class="inline-formula"><sub>2,sw</sub></span> from February to September, while total alkalinity (<span class="inline-formula"><i>A</i><sub>T</sub></span>) and sea surface salinity (SSS) explained <span class="inline-formula"><i><</i></span> 20 %. The processes controlling total inorganic carbon (<span class="inline-formula"><i>C</i><sub>T</sub></span>) partially offset this increment and explain <span class="inline-formula">∼</span> 23 %–37 % of the <span class="inline-formula"><i>f</i></span>CO<span class="inline-formula"><sub>2,sw</sub></span> seasonal change. On an interannual scale, the SST trends (0.26–0.43 °C yr<span class="inline-formula"><sup>−1</sup></span>) have accelerated by 78 %–88 % in comparison with previous decades. The ongoing surface warming contributed <span class="inline-formula">∼</span> 76 %–92 % to increasing <span class="inline-formula"><i>f</i></span>CO<span class="inline-formula"><sub>2,sw</sub></span> (4.18 to 5.53 <span class="inline-formula">µ</span>atm yr<span class="inline-formula"><sup>−1</sup></span>) and, consequently, decreasing pH (<span class="inline-formula">−</span>0.005 to <span class="inline-formula">−</span>0.007 units per year) in the surface waters. The seasonal amplitude of SST, which is becoming larger due to progressively warmer summers, was the primary driver of the observed slope of interannual trends. The evaluation of the air–sea CO<span class="inline-formula"><sub>2</sub></span> exchange shows the area across the Alboran Sea (14 000 km<span class="inline-formula"><sup>2</sup></span>) and the eastern Iberian margin (40 000 km<span class="inline-formula"><sup>2</sup></span>) acting as an atmospheric CO<span class="inline-formula"><sub>2</sub></span> sink of <span class="inline-formula">−</span>1.57 <span class="inline-formula">±</span> 0.49 mol m<span class="inline-formula"><sup>−2</sup></span> yr<span class="inline-formula"><sup>−1</sup></span> (<span class="inline-formula">−</span>0.97 <span class="inline-formula">±</span> 0.30 Tg CO<span class="inline-formula"><sub>2</sub></span> yr<span class="inline-formula"><sup>−1</sup></span>) and <span class="inline-formula">−</span>0.70 <span class="inline-formula">±</span> 0.54 mol m<span class="inline-formula"><sup>−2</sup></span> yr<span class="inline-formula"><sup>−1</sup></span> (<span class="inline-formula">−</span>1.22 <span class="inline-formula">±</span> 0.95 Tg CO<span class="inline-formula"><sub>2</sub></span> yr<span class="inline-formula"><sup>−1</sup></span>), respectively. Considering the spatial variability of CO<span class="inline-formula"><sub>2</sub></span> fluxes across the study area, a reduction of approximately 40 %–80 % in the net annual CO<span class="inline-formula"><sub>2</sub></span> sink has been estimated since 2019, which is attributed to the persistent strengthening of the source status during summer and the weakening of the sink status during spring and autumn.</p> |
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| ISSN: | 1726-4170 1726-4189 |