Marine CO<sub>2</sub> system variability along the northeast Pacific Inside Passage determined from an Alaskan ferry
<p>Information on marine CO<span class="inline-formula"><sub>2</sub></span> system variability has been limited along the northeast Pacific Inside Passage despite the region's rich biodiversity, abundant fisheries, and developing aquaculture industry. Beg...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-03-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/19/1277/2022/bg-19-1277-2022.pdf |
| Summary: | <p>Information on marine CO<span class="inline-formula"><sub>2</sub></span> system variability has been
limited along the northeast Pacific Inside Passage despite the region's rich
biodiversity, abundant fisheries, and developing aquaculture industry.
Beginning in 2017, the Alaska Marine Highway System M/V <i>Columbia</i> has served as a
platform for surface underway data collection while conducting twice weekly
<span class="inline-formula">∼1600</span> km transits between Bellingham, Washington, and Skagway,
Alaska. Marine CO<span class="inline-formula"><sub>2</sub></span> system patterns were evaluated using measurements
made over a 2-year period, which revealed the seasonal cycle as the dominant
mode of temporal variability. The amplitude of this signal varied spatially
and was modulated by the relative influences of tidal mixing, net community
production, and the magnitude and character of freshwater input. Surface
water pH<span class="inline-formula"><sub>T</sub></span> (total hydrogen ion scale) and aragonite saturation state
(<span class="inline-formula">Ω<sub>arag</sub></span>) were determined using carbon dioxide partial pressure (<span class="inline-formula"><i>p</i></span>CO<span class="inline-formula"><sub>2</sub></span>) data with
alkalinity derived from a regional salinity-based relationship, which was
evaluated using intervals of discrete seawater samples and underway pH
measurements. High-<span class="inline-formula"><i>p</i></span>CO<span class="inline-formula"><sub>2</sub></span>, low-pH<span class="inline-formula"><sub>T</sub></span>, and corrosive <span class="inline-formula">Ω<sub>arag</sub></span>
conditions (<span class="inline-formula">Ω<sub>arag</sub><1</span>) were seen during winter and
within persistent tidal mixing zones, and corrosive <span class="inline-formula">Ω<sub>arag</sub></span>
values were also seen in areas that receive significant glacial melt in
summer. Biophysical drivers are shown to dominate <span class="inline-formula"><i>p</i></span>CO<span class="inline-formula"><sub>2</sub></span> variability over
most of the Inside Passage except in areas highly impacted by glacial melt.
pH<span class="inline-formula"><sub>T</sub></span> and <span class="inline-formula">Ω<sub>arag</sub></span> extremes were also characterized based on
degrees of variability and severity, and regional differences were evident.
Computations of the time of detection identified tidal mixing zones as
strategic observing sites with relatively short time spans required to
capture secular trends in seawater <span class="inline-formula"><i>p</i></span>CO<span class="inline-formula"><sub>2</sub></span> equivalent to the contemporary
rise in atmospheric CO<span class="inline-formula"><sub>2</sub></span>. Finally, estimates of anthropogenic CO<span class="inline-formula"><sub>2</sub></span>
showed notable spatiotemporal variability. Changes in total hydrogen ion
content ([H<span class="inline-formula"><sup>+</sup></span>]<span class="inline-formula"><sub>T</sub></span>), pH<span class="inline-formula"><sub>T</sub></span>, and <span class="inline-formula">Ω<sub>arag</sub></span> over the
industrial era and to an atmospheric <span class="inline-formula"><i>p</i></span>CO<span class="inline-formula"><sub>2</sub></span> level consistent with a
1.5 <span class="inline-formula"><sup>∘</sup></span>C warmer climate were theoretically evaluated. These
calculations revealed greater absolute changes in [H<span class="inline-formula"><sup>+</sup></span>]<span class="inline-formula"><sub>T</sub></span> and
pH<span class="inline-formula"><sub>T</sub></span> in winter as opposed to larger <span class="inline-formula">Ω<sub>arag</sub></span> change in summer.
The contemporary acidification signal everywhere along the Inside Passage
exceeded the global average, with specific areas, namely Johnstone Strait
and the Salish Sea, standing out as potential bellwethers for the emergence
of biological ocean acidification (OA) impacts. Nearly half of the contemporary acidification
signal is expected over the coming 15 years, with an atmospheric CO<span class="inline-formula"><sub>2</sub></span>
trajectory that continues to be shaped by fossil–fuel development.</p> |
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| ISSN: | 1726-4170 1726-4189 |